Understanding COMPATIBILITY_LEVEL in SQL Server

I understood that setting a database to a COMPATIBILITY_LEVEL prior to your native one prevented features from being used. However this doesn't seem to be the case. Witness the following SQL script:

CREATE DATABASE Foo
GO
USE Foo
GO
ALTER DATABASE Foo SET COMPATIBILITY_LEVEL = 80
GO

CREATE TABLE Bar
(
    Id UNIQUEIDENTIFIER NOT NULL,
    TestNvcMax NVARCHAR (MAX) NOT NULL, -- Arrived in SQL 2005
    TestDateTime2 DATETIME2 (7) NOT NULL -- Arrived in SQL 2008
)
GO

But this table creates perfectly - any ideas? I would have thought some kind of an error message or warning would have been appropriate